San Jacinto Resurvey

In 1908 the Museum of Vertebrate Zoology at Berkeley mounted an expedition to the San Jacinto Mountain region, pioneering the exploration of southern California’s biology. On the 100th anniversary of this expedition, from 2008 to 2010, the San Diego Natural History Museum is retracing its path to see how the area’s wildlife has changed over the last century.

In 1908, the University of California sent out the first of its expeditions to explore the biology of California—to the San Jacinto Mountain region of Riverside County. Two teams of biologists stayed in the field continuously from May to September, traveling throughout the area, from the valley floor to the mountains’ summit, collecting vertebrates, taking copious notes and photographs, and ultimately publishing their results (Grinnell and Swarth 1913). This expedition is one of the cornerstones of understanding of southern California’s biology: it, and similar expeditions led by Joseph Grinnell to the San Bernardino Mountains in 1905–07 and along the Colorado River in 1912, were the only intensive surveys of the fauna of any area of southern California before the region was transformed forever by the flood of humanity. The expedition of 1908 thus stands as a unique benchmark, giving us the longest historic perspective possible on how the wildlife of southern California is responding to environmental change.

Since 1908, however, the biology of the San Jacinto region has not received similar attention. Some smaller areas, notably Deep Canyon, where the University of California maintains a research station, have been studied intensively, but knowledge of the region as a whole has not been kept current—in part because the 1908 expedition was so thorough. Thus the value of that expedition as a benchmark has yet to be realized.

Therefore, on the expedition’s centennial in 2008, the San Diego Natural History Museum, in cooperation with the University of California, Berkeley and Riverside, proposes an expedition retracing the steps of Joseph Grinnell and his associates in 1908. By visiting the same sites, spending a similar amount of time at each, we will be able to make a detailed comparison of how the region’s wildlife has changed over a century. Such a comparison, covering all species of vertebrates, will reveal what species may be of conservation concern on this island of montane forest, isolated by desert and urbanization.

Such a comparison will allow the effects of multiple factors to be evaluated. Urban development is encroaching on the San Jacinto Mountains from both east and west. Development of both the San Jacinto Basin to the west and the Coachella Valley to the east has already affected wildlife seriously, as recognized in the establishment of multiple-species conservation plans for both areas. Urbanization and agriculture have already touched some of the peripheral sites surveyed in 1908. The growth of Idyllwild and smaller communities within the mountains may also have affected wildlife. Some species retreat from urbanization, while others are attracted to it.

Wildfire is one of the major factors governing southern California’s biology. Our studies of the effects of the fires of 2002 and 2003 in San Diego County have already revealed many unanticipated effects on wildlife. Large fires have swept parts of the San Jacinto region recently as well. Also, suppression of fires has likely had many effects on wildlife over the past century. In San Diego County, about 25 species of woodland birds have spread south or to lower elevations in the past 100 years, possibly as a result of fire suppression. Has a similar pattern prevailed in the San Jacinto Mountains, whose central forest has not burned in recorded history?

The environmental change now looming worldwide is the warming of the climate. In southern California, temperature change so far has been reflected largely in increased winter low temperatures at high elevations and in increased summer high temperatures in the desert (L. J. Hargrove and P. Unitt analysis of U.S. Weather Service data). These changes may be expected to lead to changes in animals’ distribution and life history. At high elevations, mammals may remain active longer or cease hibernating entirely; birds may nest earlier in the year, winter at higher elevations, or dispense with migration; the distributions of thermally dependent reptiles may expand or contract. At low elevations, with higher temperatures, some mammals and reptiles may estivate longer, while other animals of all classes may be so heat-stressed they are unable to reproduce or survive in parts of their former ranges. In the Yosemite region, the scientists from the Museum of Vertebrate Zoology (MVZ) at the University of California, Berkeley, have retraced the paths of another early expedition and found many changes, even in the wilderness. Many of these changes, such as the upslope spread of the pinyon mouse (Peromyscus truei) and the upslope contraction of the pika (Ochotona princeps) and alpine chipmunk (Tamias alpinus), appear linked to climate warming.

In the southwestern U.S., another predicted change is decreased rainfall. Prolonged drought is likely to lead to great change in animals’ abundance and ranges as well. Following the extremely dry winter of 2001–02, the nesting of four species of birds near San Diego decreased almost to zero (Bolger et al. 2004), and in areas of San Diego County burned in 2002 and 2003 the abundance of many species of birds and mammals has fluctuated more in response to variations in rainfall than it has to postfire recovery of vegetation (P. Unitt and S. Tremor unpubl. data).

Thus, by replicating the effort of Joseph Grinnell, Harry Swarth, Walter Taylor, and Charles Richardson we will realize the value of their work as a benchmark and establish a basis of comparison for future changes at a critical moment in history. As Grinnell himself wrote concerning the value of his work: “This value will not, however, be realized until the lapse of many years, possibly a century, assuming that our material is safely preserved. And this is that the student of the future will have access to the original record of faunal conditions in California and the West, wherever we now work.”

Coordination of our proposed resurvey of the San Jacinto region with the methods being used by MVZ elsewhere in California will allow changes to be assessed and predictions of future change to be made at an even broader scale. Scientists from MVZ have already developed the techniques and models from which these comparisons and predictions can be made.